Can I e-file an amend to my accepted e-filed 2020 tax?

Can I e-file an amend to my accepted e-filed 2020 federal 1040 tax return after 10/15/2021? IRS says amend e-file is available for 2019 and 2020 1040s, but my turbo tax (Mac version) said I can’t. Today’s date is 10/20/2021. If yes, could you please send me the instructions?